Year	Percent
1960	23.57163
1961	21.75397
1962	18.02027
1963	17.92221
1964	19.49015
1965	18.16354
1966	18.96125
1967	17.90348
1968	18.48384
1969	18.37762
1970	17.63698
1971	16.95332
1972	18.574
1973	20.83671
1974	27.55665
1975	22.47288
1976	17.91505
1977	16.89596
1978	16.37089
1979	17.01014
1980	19.33593
1981	22.67121
1982	21.60474
1983	22.7547
1984	25.63418
1985	25.51323
1986	21.88237
1987	22.48125
1988	24.99655
1989	22.55494
1990	24.55932
1991	22.31877
1992	22.17215
1993	22.06075
1994	20.9385
1995	22.67322
1996	21.83597
1997	23.92412
1998	23.4038
1999	25.15437
2000	26.78743
2001	28.20917
2002	28.91761
2003	27.50378
2004	28.1076
2005	30.91916
2006	32.75536
2007	34.57168
2008	35.74235
2009	28.00317
2010	32.23302
2011	34.70003
2012	34.92955
2013	32.77764
2014	34.33262
2015	34.29425
2016	35.09028
2017	36.77561